Anisotropic Wetting Surfaces with One‐Dimesional and Directional Structures: Fabrication Approaches, Wetting Properties and Potential Applications

Abstract

This review article provides a brief summary of recent research progress on anisotropic wetting on one-dimensional (1D) and directionally patterned surfaces, as well as the technical importance in various applications. Inspiration from natural structures exhibiting anisotropic wetting behavior is first discussed. Development of fabrication techniques for topographically and chemically 1D patterned surfaces and directional nanomaterials are then reviewed, with emphasis on anisotropic behavior with topographically (structurally) patterned surfaces. The basic investigation of anisotropic wetting behavior and theoretical simulations for anisotropic wetting are also further reviewed. Perspectives concerning future direction of anisotropic wetting research and its potential applications in microfluidic devices, lab-on-a-chip, sensor, microreactor and self-cleaning are presented.

Fabrication of an Anisotropic Superhydrophobic Polymer Surface Using Compression Molding and Dip Coating

“…The water droplet could move along the microscale groove patterns more easily because of the lower SA || . This phenomenon is comparable to rice leaves [1,13]. After coating, the apparent contact angles in both directions were higher than 150° and the apparent contact angles did not show any clear differences.…”

“…In nature, rice leaves and butterfly wings have special anisotropic wettability and the water droplet can be easily moved along a certain direction, such as the direction parallel to the leaf edge in rice leaves or the radial outward direction of the body's central axis in butterfly wings. This anisotropic superhydrophobic surface is important for liquid transport and liquid interactions on the surface for specific functionality such as self-cleaning of dust on a rice leaf and the prevention of water contact on the butterfly body [1,13]. This anisotropic wetting property can be realized mainly using structural patterned surfaces with nano or microscale parallel lines or grooves.…”

“…The lines or grooves have been fabricated by lithography, embossing, imprinting, laser machining, the formation of wrinkles via mechanical compressing, or other fabrication methods [13,[18][19][20][21][22][23][24][25][26][27][28]. For mass production of an anisotropic wetting surface, replication of patterns using a mold seems to be suitable, but many studies have used poly(methyl methacrylate) (PDMS), which has a relatively long curing time and limited reusability of the mold [13,[18][19][20][21], and molds with an uncontrollable surface roughness and side wall slope by laser machining and wrinkle formation, which does not show a clear pattern shape [7][8][9][10][11]13]. Additionally, the high surface energy ink pattern printing method can create various anisotropic superhydrophobic surfaces with low cost and large scale production especially 2D paper based applications [29].…”

External‐Field‐Induced Gradient Wetting for Controllable Liquid Transport: From Movement on the Surface to Penetration into the Surface

“…[1][2][3][4][5][6][7][8] The liquid-wetting behavior on a solid or liquid surface is mainly dependent on the chemical composition and surface roughness, which play important roles in liquid transport. [9][10][11][12][13][14][15][16] The wettability gradient of a surface for a liquid droplet with an asymmetrical contact angle (CA) can produce a driving force for liquid motion, which is generally generated by introducing a chemical or structure gradient. [17][18][19][20][21][22][23][24][25][26][27][28] External-field-responsive liquid transport has received extensive research interest owing to its important applications in microfluidic devices, biological medical, liquid printing, separation, and so forth.…”

Surface Textured Polymer Fibers for Microfluidics

“…[ 15 ] Although these techniques have shown to be very successful for shaping material at the microscale, they are impractical for fabrication of affordable microfl uidic systems. In addition, fabrication of three-dimensional architectures, which is particularly important for compact and multicomponent microfl uidic devices, is challenging with lithography based methods.…”